Modern vehicles contain a relatively large number of electric actuators with which the rotational movement generated by an electric motor that can be actuated by a control device is converted into a linear or rectilinear movement of the vehicle component that is to be moved. A special area of application of such actuators is in the automatic actuation of a starting and shifting clutch of a motor vehicle, whereby the component that is to be actuated can be, for example, a so-called central clutch release device of the friction clutch. During actuation, such a central clutch release device acts, for example, on the diaphragm spring of the clutch in such a way that it is released or brought into a slip position in which the clutch can transmit no torque at all or only a reduced torque from the drive engine of the vehicle to the gear.
Various deflection gears have become known for purposes of converting the rotational movement of the rotor of the electric motor into a rectilinear movement. Thus, for example, deflection gears are used in conjunction with actively controllable multi-disk clutches and these deflection gears are used on axle or middle differentials as differential locks and in a power train with selectable four-wheel drive as a selectable clutch of a drive axle that can be activated as needed. By means of the deflection gear, an externally generated controlling torque is continuously converted at a high transmission ratio into an axial contact force in order to actuate, that is to say, in order to at least partial close, an associated multi-disk clutch.
Two embodiments of a differential gear with a disk lock that can be actuated by means of an electric motor via such a deflection gear are described in EP 0 368 140 B1. According to a first embodiment, in FIG. 1, the differential gear is configured with a bevel wheel design. A support ring is drive-connected via a bevel wheel of a reduction gear to an electric motor that is affixed to the housing. An adjusting ring is mounted non-rotatably and axially movably on the housing side and is connected directly to the support ring via cam tracks. Hence, a rotation of the support ring is converted into an axial movement of the adjusting ring which is connected—via an axial thrust bearing, via an outer pressure plate that rotates together with the differential cage via several tappets that penetrate the differential cage and via an inner pressure plate—to the multi-disk clutch, whose disks are arranged operatively between the differential cage and one of the two output bevel wheels.
In a second variant according to FIG. 2 in the above-mentioned application, the differential gear is configured with a planetary design. The support ring here is mounted non-rotatably and axially immovably on the housing side. In contrast, the adjusting ring is mounted rotatably and axially movably and, on the one hand, it is drive-connected via the pinion of a reduction gear to an electric motor that is affixed to the housing, and on the other hand, it is connected to the support ring via several ball grooves that ascend on the circumference side and via rolling elements arranged therein. Therefore, a rotation of the adjusting ring is converted by a rolling movement of the rolling elements between the opposing axially ascending ball grooves into an axial movement of the adjusting ring which is connected—via an outer axial thrust bearing, via an outer pressure plate that rotates together with the differential cage, via several first tappets that penetrate the differential cage, via a first inner pressure plate, via an inner axial thrust bearing, via a thrust washer, via several second tappets that penetrate the center pin of the planetary carrier and via a second inner pressure plate—to the multi-disk clutch, whose disks are arranged operatively between the differential cage and the sun wheel of the differential gear.
Another differential gear with a disk lock that can be actuated by means of an electric motor via a similar deflection gear is known from U.S. Pat. No. 4,805,486 A. With this differential gear, a support ring is mounted non-rotatably and axially immovably on the housing side. An adjusting ring is supported rotatably as well as axially movably, and on the one hand, it is drive-connected via the pinion of a reduction gear to an electric motor that is affixed to the housing and, on the other hand, it is connected—either via cam surfaces that ascend on the circumference side (see FIG. 2 there) or via ramp surfaces that ascend on the circumference side and via rolling elements arranged therein (see FIG. 3 there)—to the support ring. A rotation of the adjusting ring is thus converted by a sliding movement of the opposing axially ascending cam surfaces or by a rolling movement of the rolling elements between the opposing axially ascending ramp surfaces into an axial movement of the adjusting ring which is connected—via an outer axial thrust bearing, via an outer pressure plate, via several pistons that penetrate the differential cage and via an inner pressure ring—to the multi-disk clutch, whose disks are arranged operatively between the differential cage and one of the two output bevel wheels of the differential gear.
Only for the sake of completing the known state of the art, reference is hereby made to German patent application DE 103 48 312 A1 that discloses an actuation device for a friction coupling device with which a clutch actuator equipped with the described ball ramps can be actuated by means of a bowden cable.
All of these known deflection gears have in common the fact that the axially ascending ramp and cam surfaces are oriented towards the circumference. As a consequence, the corresponding operative contours are each limited to a relatively small rotational angle sector of the input element, disadvantageously resulting in a relatively small transmission ratio between the rotational movement and the torque of the input element as well as the axial movement and the axial contact force of each associated output element. A precise setting of a desired locking power or closing power by means of the axial contact force acting on the appertaining multi-disk clutch is thus hardly possible and moreover, presupposes a considerable absence of play on the transmission path between the electric actuating drive and the input element. Moreover, there is a need for a very precise manufacture of the cam or ramp surfaces of the input element and output element, as a result of which the production of this component is complicated and hence expensive.